1. Field of the Invention
This invention relates to new rhodium compounds and a process for producing the same. More particularly, it is concerned with new rhodium compounds having a structure isoelectronic to HRh(CO)(PPh.sub.3).sub.3 and a process for the selective production of the same. Further, it relates to use of such products as catalysts in the oxo process.
2. Description of the Prior Art
Carbonyl tris (triphenylphosphine) rhodium hydride is known as a catalyst having activity in various chemical reactions for organic syntheses, for example, in hydroformylation. (Japanese Patent Publication No. 10730/1970 equivalent to U.S. Pat. No. 3,527,809). See also U.S. Pat. No. 3,821,311 and Canadian Patent 992,101. As rhodium compounds having a structure isoelectronic thereto are known carbonyl tris(triphenylphosphite) rhodium hydride HRh(CO)(P(OPh).sub.3).sub.3 (British Pat. No. 1338225), carbonyl tris(triphenylarsine) rhodium hydride HRh(CO)(AsPh.sub.3).sub.3 and carbonyl tris (triphenylarsite) rhodium hydride HRh(CO)(As(OPh).sub.3).sub.3 (British Patent No. 1357735). As to producing these compounds, some processes are known. In the case of HRh(CO)(PPh.sub.3).sub.3, for example, there have been proposed (1) a process comprising reacting rhodium trichloride trihydrate, excess triphenylphosphine, an aqueous solution of formaldehyde and sodium borohydride in boiling ethanol (Journal of the Chemical Society (A), 1968, page 2660), (2) a process comprising reacting carbonyl bis(triphenylphosphine) rhodium chloride, excess triphenylphosphine and sodium borohydride in boiling ethanol (ibid) and (3) a process comprising contacting carbonyl bis(triphenylphosphine) rhodium chloride and excess triphenylphosphine with synthesis gas (mixture of H.sub.2 and CO) at a temperature of at least 55.degree. C. under a pressure of at least 10 atm. (Japanese Patent Publication No. 17572/1978).
However, carbonyl tris(triphenylstibine) rhodium hydride HRh(CO)(SbPh.sub.3).sub.3 having a structure isoelectronic to the above described rhodium compounds has not been synthesized and isolated. Moreover, as is evident from the foregoing description, all the rhodium compounds having the above described known structures contain respectively a single kind of ligand and those containing different kinds of mixed ligands, for example, phosphines and arsines in the same molecule, are not known, although some monovalent rhodium compounds containing mixed ligands in the same molecule are known, for example, carbonyl triphenylphosphine triphenylarsine rhodium chloride RhCl(CO)(PPh.sub.3) (AsPh.sub.3) (Journal of Organometallic Chemistry, Vol. 43, No. 2, 1972, page 425), carbonyl triphenylphosphine triphenylstibine rhodium chloride RhCl(CO)(PPh.sub.3)(SbPh.sub.3) (ibid), carbonyl triphenylarsine triphenylstibine rhodium chloride RhCl(CO)(AsPh.sub.3)(SbPh.sub.3) (ibid) and carbonyl (diethylphenylphosphine) (tri-o-toluylstibine) rhodium chloride RhCl(CO)(PPhEt.sub.2)(Sb(o-CH.sub.2 C.sub.6 H.sub.4).sub.3) (Inorganic Chemistry, Vol. 15, No. 13, 1976, page 646). See also J. Chem. Soc. D1970, (17), 1077-8 (England); Inorg. Nucl. Chem. Lett. 1971, 7(9)877-9 (England); J. Chem. Soc. Dalton Trans. 1972 (19) 2161-9 (England) and U.S. Pat. No. 3,459,780. As a method for synthesizing these compounds, it has been proposed to add to a binuclear rhodium compound (RhCl(CO)L).sub.2 wherein L is triphenylphosphine, triphenylarsine or triphenylstibine in warm benzene an ether solution of 2 mols (equimolar amount) of L' being triphenylphosphine, triphenylarsine or triphenylstibine but not the same as L (Journal of Organometallic Chemistry, Vol. 43, No. 2, 1972, page 425).
Other references of lesser interest, noted because they concern rhodium-containing compounds, are U.S. Pat. Nos. 3,939,188 and 3,946,082, which relate to compounds containing reduced, zero valent rhodium and 4,052,461 which relates to ionic rhodium compounds but not the hydrides which are non-ionic.
However, mixed ligands-containing rhodium compounds having a structure isoelectronic to HRh(CO)(PPh.sub.3).sub.3 or three stibines-coordinated rhodium compounds cannot be obtained, or mixtures of various rhodium compounds are only obtained, by the above described method or other known methods and it is very difficult to isolate such compounds in a pure form.
Rhodium phosphine type or rhodium-phosphite type complexes are known as catalysts for the hydroformylation of olefins. The stability of a rhodium catalyst is increased by modification with phosphine, arsine, or stibine, which permits practicing the oxo reaction at a rather low pressure.
According to Japanese Pat. No. 903,326, straight chain-rich aldehydes are prepared at a low total pressure with a low partial pressure of carbon monoxide and a high partial pressure of hydrogen in the presence of a rhodium triarylphosphine catalyst and a triarylphosphine ligand in a large excess to the rhodium. However, this method has the disadvantage that the hydroformylation reaction rate of an olefin is markedly decreased because of using a ligand in a large excess to rhodium, and a considerable quantity of a paraffin is formed by the hydrogenation of the olefin ("Hydrocarbon Processing" (4) 112 (1970)) due to the reaction at a low total pressure with a low partial pressure of carbon monoxide and a high partial pressure of hydrogen.
Rhodium catalysts in combination with arsines or stibines instead of phosphines have been proposed, but the studies thereof have not been made so intensively because of their lower activity compared with tertiary phosphine-rhodium catalysts.